Faulty type inference for `Enum` attributes

[harahu]

Bug Report

Accessing an instance of an enum though another instance leads to the wrong type being inferred for the instance.

To Reproduce

See: https://mypy-play.net/?mypy=master&python=3.12&flags=disallow-any-unimported&gist=26f57e606e831442885c45110b8d8650

import enum

class Color(enum.Enum):
    RED = "RED"
    GREEN = "GREEN"
    BLUE = "BLUE"

c = Color.RED

# error: Incompatible types in assignment (expression has type "str", variable has type "Color")  [assignment]
c = c.GREEN

Expected Behavior

I expect mypy to understand that c.GREEN is also of type Color.

Actual Behavior

Mypy thinks c.GREEN is of type str.

main.py:11: error: Incompatible types in assignment (expression has type "str", variable has type "Color")  [assignment]
Found 1 error in 1 file (checked 1 source file)

Your Environment

• Mypy version used: master (post 1.3.0 at time of writing)
• Mypy command-line flags: n/a
• Mypy configuration options from mypy.ini (and other config files): n/a
• Python version used: 3.12

[blbelew]

This is affecting me as well, but triggering a "Statement is unreachable" error when warn_unreachable = True is in my mypy.ini. Consider the following (using the previous color enum):

import enum

class Color(enum.Enum):
    RED = "RED"
    GREEN = "GREEN"
    BLUE = "BLUE"

def test(c:Color) -> str:
    if c == c.RED:
        return "it's red"
    if c == c.GREEN:
        return "it's green"
    if c == c.BLUE:
        return "it's blue"

    return "unknown color"

MyPy 1.3.0 doesn't complain about this code, but MyPy 1.4.0 gives "Statement is unreachable" errors for each of the three conditional returns.